HIP | FEATURE: HOT WATER CYLINDERS
HOT WATER CYLINDERS: THE BASICS There are a wide range of cylinders on the market today, but when it comes to selecting the right one, a number of factors need to be considered. Here, the Association of Plumbing and Heating Contractors (APHC), explains some of the basic differences. TYPES OF HOT WATER STORAGE CYLINDERS
WHAT TO CONSIDER
There are essentially two types of cylinder: Direct and Indirect.
The following requirements need to be understood prior to installation: ■ Quantity of hot water required ■ Temperature required at outlets and the temperature of stored water ■ Cost of installation and maintenance ■ Fuel energy requirements ■ Wastage of water and energy running costs ■ User safety: such as scalding water, over pressurisation and legionella bacteria
DIRECT
This is a hot water storage cylinder which has a large open space inside it. They should only be used in a hot water system where the components are not subject to corrosion by fresh water. They’re therefore not suitable to be installed in combined heating and hot water systems where there is a range of metallic materials such as steel (radiators) which corrode in the presence of fresh water. They tend to be used in modern systems when the hot water is heated by electricity (immersion heaters).
“AN OPEN VENTED HOT WATER CYLINDER IS FED FROM A COLD WATER CISTERN.”
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INDIRECT
This type of hot water storage cylinder includes a coil inside it. The coil is used to transfer heat from a boiler or heat pump circuit, keeping the fresh water to be heated in the cylinder and distributed to the taps, completely separate from the heated water supply from the boiler or heat pump circuit.
